The Institution Number is also assigned to the user's User Group, but has very specific restrictions for certain global system settings. These specific restrictions are which overlay is available to the user for each Document Type, and which class(es) of service are available to the user during Document Distribution.
User Groups are restricted on an institutional basis. The User Groups from one institution can not be accessed/modified by a user with rights from another institution. The exception to this is the database's designated super user or administrator.